1. Field of the Invention
The present invention relates to a preheating system for a Diesel engine, and more particularly to a preheating system for heating a preheating or glow plug of a Diesel engine to facilitate engine starting.
2. Description of the Prior Art
In a Diesel engine having a preheating or glow plug, before cranking the engine by driving a starter motor, the preheating plug is energized to become heated to a temperature at which the starter motor is started. The time required for the preheating depends mainly upon temperatures of the engine. For example, at a temperature higher than 20.degree. C. the preheating time is less than a few seconds, and at -20.degree. C. it becomes as much as 60 seconds. Accordingly, the engine can readily be started for a short period of time in warm environments or in summer season without requiring the preheating, while in cold environments or in winter preheating for a long time is required.
In general, a switch for energizing the preheating plug is integrally provided in an engine starter switch. An engine key is inserted into the starter switch and rotated to a preheating position and after a determined period of time has been lapsed the engine key is rotated to a starting position.
In starting a Diesel engine, a driver opens a door of a vehicle, sits on a seat, wears seat belts, inserts an engine key into a switch and operates the switch to preheat a preheating or glow plug and, after a completion of the preheating, further operates the switch to drive a starter motor. The time for the completion of the preheating is as much as 40-60 seconds in cold season for example at atmospheric temperature -10.degree. to -20.degree. C. During such a period of time, the driver must wait for the lapse of time sitting on the cold seat which may be uncomfortable and troublesome. Thus, Diesel engine cars have not been acceptable although they have various advantages.
When the temperature of the engine is relatively high, only a short period of time for the preheating is required. With such a relatively high temperature, however, a starting of the engine without any preheating is rather unfavorable; starting may be remarkably improved by a preheating of a short period such as a few seconds. Since a driver usually wishes to start the engine as early as possible, he is apt to neglect the preheating, if it is possible.
It has been proposed to begin the preheating by opening a door of a vehicle. However, the door is frequently opened other than in starting the engine, so that a glow plug is unduely heated every opening of the door resulting in its failure.
Even after the start of an engine, the engine tends to stall if its temperature is not sufficiently high. If it does not stall, the combustion rate of a fuel is low, making a nuisance of noise and smoky exhaust gases.
To solve this problem, it has been proposed to continue preheating a glow plug for a period of time after start of an engine thereby improving the starting performance of a Diesel engine. Such a process is referred to as "after-glowing" system.
With this system, however, it is required to provide delay means for continuing to supply a current to the glow plug for the period of time after the start of the engine. Such delay means are a temperature sensor which senses the temperature in the engine to be a determined one and a switch adapted to be operated when the vehicle reaches a predetermined speed. These means are expensive and poor in practical usefulness for lack of durability.
In usual preheating system, a driver visually confirms how a preheating or glow plug has been heated by means of a glow lamp and thereafter starts an engine.
With the recent progress of the technical field, it becomes possible to start an engine at a normal temperature without heating the glow plug. However, the time required for cranking a starter motor is long and therefore there is a tendency for durability of a battery and driving system to be shortened.
With the popularization of Diesel engine cars, moreover, unskilled drivers would fail in judgement of the preheated condition by estimating the brightness of glow lamps and start engines under insufficiently preheated conditions with resulting more elongated cranking time. At a low temperature, such as lower than 10.degree. C., the preheating becomes more important and the start of the engine is very difficult under the insufficiently preheated condition.
The driver's judgement of preheating by evaluating the brightness of the glow lamp is generally unreliable. Moreover, it is painful for the driver to notice the glow lamp in a cold vehicle for several tens of seconds and during this period of time the driver cannot turn his attention to other operations.